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Tsunami survival: Emergency shelters needed
REUTERS/Asahi Shimbun
SPECIAL REPORT / Japanese quake AT 2.46 pm local time on Friday last week, Japan shook like never before. The magnitude 9.0 earthquake wrenched the main island of Honshu 2.5 metres closer to the US and nudged the tilt of Earth’s axis by 16 centimetres. At the epicentre, 130 kilometres offshore, the Pacific tectonic plate lurched westwards, and a 10-metre-high tsunami sped towards the coastal city of Sendai and the surrounding region. The devastation caused by the events is difficult to exaggerate – estimates suggest the number of fatalities could top 10,000. One of the few consolations is that quakes of magnitude 8.5 and above are rare: the Sendai earthquake is in the top 10 of the highest-magnitude quakes of the last 100 years. Yet three of these – the December 2004 Sumatra quake, the February 2010 Chile quake, and now Sendai – have struck in just over six years. This presents a horrifying possibility: that there is a link between these megaquakes and that, as a result, more could strike. Most geologists say that the number of megaquakes is too small to be able to make a statistically convincing case for a link. “You will get a lot of different answers from different people, but inevitably the ability of any one of those to convince everyone else that they’re right is going to depend on the statistics of small numbers,” says Ross Stein of the US Geological Survey (USGS) in Menlo Park, California, “and we’re never going to get anywhere.” A handful, however, feel there must be a link between recent events. “What is clear is that for the 6.2 years since 2004, there have been more great earthquakes around the world than in any 6.2-year period throughout the 110-year history of seismic recordings,” says Thorne Lay at the University of California, Santa Cruz. His colleague Emily Brodsky goes further: “The recent spurt of magnitude-8-plus earthquakes may be an extended aftershock sequence of the 2004 Sumatra earthquake.” While demonstrating a domino effect is a challenge, Lay does have a geological mechanism that can link some large quakes that occur several months apart. He cites doublets – pairs of comparably large quakes 6 | NewScientist | 19 March 2011
megaquake aftermath
The biggest earthquake in Japanese history and the ensuing tsunami has left thousands dead and many more missing. As Japan faces its worst crisis since the second world war, New Scientist examines the evidence that giant earthquakes are linked and, overleaf, explores what must be done to protect nuclear reactors in seismic zones
Kuril Islands 15 November 2006
Magnitude 8.3
13 January 2007
Magnitude 8.1
Sichuan, China 12 May 2008
Magnitude 8.0
JUAN DE FUCA PLATE
Sendai, Japan 11 March 2011
EURASIAN PHILIPPINE PLATE PLATE
Magnitude 9.0
PACIFIC PLATE
Sumatra, Indonesia
NORTH AMERICAN PLATE
CARIBBEAN PLATE
COCOS PLATE
NAZCA PLATE
26 December 2004
Magnitude 9.1
Maule, Chile
INDIAN PLATE
27 February 2010
Magnitude 8.8
It is hard to overstate the extent of the devastation in Japan
ANTARCTIC PLATE
For updates on this story, visit www.NewScientist.com/special/japanquake
How can you protect against a tsunami? OF ALL nations, Japan was perhaps the best prepared to withstand a tsunami. But as last week’s terrible loss of life has shown, better shelters are sorely needed. Building towers and berms – artificial embankments – that can provide high ground for residents of low-lying areas is difficult and expensive. Brahman Developments of San Juan, Puerto Rico, has proposed an innovative and affordable alternative: a submarine-shaped reinforced concrete structure that would literally ride the waves, keeping up to 80 people safe inside. Known as the STATIM Shelter System, the tubular structures would be tethered, but could float freely. They are designed to survive temporary submersion and to be self-righting. Built from reinforced concrete, they should also be sturdy enough to survive being battered with debris in a major tsunami. It’s like “an inland lifeboat”, says inventor Miguel Serrano of Brahman. “It’s not a fun ride, but you would survive.” The company projects that each shelter would cost about $100,000 and could be equipped with communications systems, GPS and enough food and water for inhabitants to survive for up to a week without aid. They could be deployed every few blocks in densely populated areas. That’s an appealing prospect, given that many of those who perished in Japan were
elderly people who lacked the mobility to flee to higher ground. Japan already has some permanent structures designed as tsunami escape havens. Nishiki Tower in Mie prefecture, for instance, is five storeys tall and doubles as a public toilet, museum and storage space. While more such structures are needed, Japan is well ahead of the rest of the world. In the US’s Pacific northwest, for instance, city leaders are just starting to plan for a tsunami that could be generated by a rupture of the Cascadia fault – which threatens an earthquake of magnitude 9.0 or greater. Cannon Beach, Oregon, has an ageing city hall that it hopes to tear down and rebuild as a state-of-the-art tsunami refuge. The building would have sea walls to the front and rear, says Yumei Wang, a geotechnical engineer for the state, and sit upon concrete pillars reinforced with tension steel cables. These would allow water and debris from a tsunami to pass underneath while local residents take refuge on the upper floor and roof. Long Beach, Washington, meanwhile, is considering building a berm next to the town’s elementary school. It would normally provide a grassy slope for spectators to watch school sports, but provide shelter for up to 1000 people should a tsunami strike. Sujata Gupta
that happen on the same or neighbouring faults within months of each other. In November 2006, an 8.3-magnitude quake shook the Kuril Islands north of Japan as the Pacific plate pushed beneath them. Two months later, in January 2007, the islands felt the force of a second large quake, this time an 8.1-magnitude event. When the Pacific plate lunged beneath the islands in the first of those quakes, it left the oceanic crust under tension. The January quake was the result of a new rupture that allowed the plate to stretch and thin to compensate (Nature, vol 451, p 561; and see diagram, page 8). Doublets like this show that large earthquakes months apart and on separate faults can be linked by a sound geological mechanism. It does not prove that this is also true of events separated by longer periods and greater
distances. For this, Lay says you would want to show, for instance, that a region which has experienced a large quake recorded unusual seismic activity and perhaps even some small tremors during a previous large event elsewhere on the planet. This might suggest that the earlier event unsettled a fault, effectively priming it. For an example, Lay cites the 7.9-magnitude event that hit Sichuan in China in May 2008. “The 2004 Sumatra earthquake increased seismicity in that area as the [shock] waves passed by,” he says. “Was the 2008 earthquake a delayed, large aftershock, or a totally independent event?” The trouble is that large earthquakes generate tectonic waves that ripple around the world’s surface and routinely trigger smaller quakes on distant faults, so increased activity > 19 March 2011 | NewScientist | 7
SPECIAL REPORT / Japanese quake
Seismic zones shake out nuclear problems
Doublet danger Stretching opens a new fault in the plate, causing a second large quake
“IT’S LIKE a kamikaze terrorist wrapped in bombs just waiting to explode.” That’s how Kobe University seismologist Katsuhiko Ishibashi described Hamaoka, a nuclear power plant situated to the south-east of Tokyo. Straddling the subduction zone between two tectonic plates, it may be the most dangerous nuclear plant in Japan. While that plant was unaffected by the magnitude 9.0 quake on 11 March, the explosions and radiation released at the Fukushima Daiichi nuclear power station this week look set to place the wisdom of siting such plants in quake zones under far greater scrutiny. The UN’s International Atomic Energy Agency says 88 of the world’s 442 nuclear power stations are in seismically active areas – including two in California: the San Onofre plant near San Diego and Diablo Canyon near San Luis Obispo.
STRESSED TECTONIC PLATE RUPTURES KURIL ISLANDS
PACIFIC PLATE TRENCH
15 November 2006 Magnitude
8.3
13 January 2007 Magnitude
8.1
in China is hardly a surprise. “If you have a quake of, let’s say, 6.2 or larger, every sand grain on the planet is moving to the music of that event,” Stein says. Perhaps the biggest stumbling block to proving that large earthquakes trigger others on a global scale is statistics. To find out if quakes really do cluster in a non-random way, Tom Parsons, also at the USGS in Menlo Park, and Aaron Velasco at the University of Texas at El Paso, crunched some numbers. They compensated for the rarity of megaquakes by widening their focus to events of magnitude 7 and higher. The pair then searched for statistical links between these quakes “Meltdown and others of magnitude 5 and above becomes a around the world. risk if water After reviewing a 30-year catalogue evaporates of events, they found no significant faster than it evidence that large quakes regularly trigger tectonic activity 1000 kilometres is pumped into the reactor” or more away. Discussions over the clustering of megaquakes will rumble on. Unfortunately for the people of Japan, what is beyond doubt is that large quakes can cluster locally: aftershocks are common in the wake of a large quake, and occasionally they can be as large as the primary shock. “We are in a cluster right now and it’s centred on Japan,” says Stein. “Japan could be in for other big quakes in the wake of this one. That part we should agree on.” Catherine Brahic n 8 | NewScientist | 19 March 2011
reuters
SUBDUCTION
“Nuclear regulatory agencies will want to re-examine the potential for tsunami risks to nuclear power plants, certainly on the Pacific Rim and possibly in other oceans as well,” says John Stevenson of the IAEA’s International Seismic Safety Centre. While power companies already estimate the risk from tsunamis based on the geological record, Stevenson admits that “there is always the chance that what has been experienced in the past will be exceeded”. That’s what happened at Fukushima. When the quake struck, seismic sensors tripped on the three working reactors, sending neutron-absorbing boron control rods into their cores to shut them down. It doesn’t end there, though. Residual heat from each reactor’s nuclear pile still has to be carried away by the electrically
SPECIAL REPORT / Japanese quake AT 2.46 pm local time on Friday last week, Japan shook like never before. The magnitude 9.0 earthquake wrenched the main island of Honshu 2.5 metres closer to the US and nudged the tilt of Earth’s axis by 16 centimetres. At the epicentre, 130 kilometres offshore, the Pacific tectonic plate lurched westwards, and a 10-metre-high tsunami sped towards the coastal city of Sendai and the surrounding region. The devastation caused by the events is difficult to exaggerate – estimates suggest the number of fatalities could top 10,000. One of the few consolations is that quakes of magnitude 8.5 and above are rare: the Sendai earthquake is in the top 10 of the highest-magnitude quakes of the last 100 years. Yet three of these – the December 2004 Sumatra quake, the February 2010 Chile quake, and now Sendai – have struck in just over six years. This presents a horrifying possibility: that there is a link between these megaquakes and that, as a result, more could strike. Most geologists say that the number of megaquakes is too small to be able to make a statistically convincing case for a link. “You will get a lot of different answers from different people, but inevitably the ability of any one of those to convince everyone else that they’re right is going to depend on the statistics of small numbers,” says Ross Stein of the US Geological Survey (USGS) in Menlo Park, California, “and we’re never going to get anywhere.” A handful, however, feel there must be a link between recent events. “What is clear is that for the 6.2 years since 2004, there have been more great earthquakes around the world than in any 6.2-year period throughout the 110-year history of seismic recordings,” says Thorne Lay at the University of California, Santa Cruz. His colleague Emily Brodsky goes further: “The recent spurt of magnitude-8-plus earthquakes may be an extended aftershock sequence of the 2004 Sumatra earthquake.” While demonstrating a domino effect is a challenge, Lay does have a geological mechanism that can link some large quakes that occur several months apart. He cites doublets – pairs of comparably large quakes 6 | NewScientist | 19 March 2011
megaquake aftermath
The biggest earthquake in Japanese history and the ensuing tsunami has left thousands dead and many more missing. As Japan faces its worst crisis since the second world war, New Scientist examines the evidence that giant earthquakes are linked and, overleaf, explores what must be done to protect nuclear reactors in seismic zones
Kuril Islands 15 November 2006
Magnitude 8.3
13 January 2007
Magnitude 8.1
Sichuan, China 12 May 2008
Magnitude 8.0
JUAN DE FUCA PLATE
Sendai, Japan 11 March 2011
EURASIAN PHILIPPINE PLATE PLATE
Magnitude 9.0
PACIFIC PLATE
Sumatra, Indonesia
NORTH AMERICAN PLATE
CARIBBEAN PLATE
COCOS PLATE
NAZCA PLATE
26 December 2004
Magnitude 9.1
Maule, Chile
INDIAN PLATE
27 February 2010
Magnitude 8.8
It is hard to overstate the extent of the devastation in Japan
ANTARCTIC PLATE
For updates on this story, visit www.NewScientist.com/special/japanquake
How can you protect against a tsunami? OF ALL nations, Japan was perhaps the best prepared to withstand a tsunami. But as last week’s terrible loss of life has shown, better shelters are sorely needed. Building towers and berms – artificial embankments – that can provide high ground for residents of low-lying areas is difficult and expensive. Brahman Developments of San Juan, Puerto Rico, has proposed an innovative and affordable alternative: a submarine-shaped reinforced concrete structure that would literally ride the waves, keeping up to 80 people safe inside. Known as the STATIM Shelter System, the tubular structures would be tethered, but could float freely. They are designed to survive temporary submersion and to be self-righting. Built from reinforced concrete, they should also be sturdy enough to survive being battered with debris in a major tsunami. It’s like “an inland lifeboat”, says inventor Miguel Serrano of Brahman. “It’s not a fun ride, but you would survive.” The company projects that each shelter would cost about $100,000 and could be equipped with communications systems, GPS and enough food and water for inhabitants to survive for up to a week without aid. They could be deployed every few blocks in densely populated areas. That’s an appealing prospect, given that many of those who perished in Japan were
elderly people who lacked the mobility to flee to higher ground. Japan already has some permanent structures designed as tsunami escape havens. Nishiki Tower in Mie prefecture, for instance, is five storeys tall and doubles as a public toilet, museum and storage space. While more such structures are needed, Japan is well ahead of the rest of the world. In the US’s Pacific northwest, for instance, city leaders are just starting to plan for a tsunami that could be generated by a rupture of the Cascadia fault – which threatens an earthquake of magnitude 9.0 or greater. Cannon Beach, Oregon, has an ageing city hall that it hopes to tear down and rebuild as a state-of-the-art tsunami refuge. The building would have sea walls to the front and rear, says Yumei Wang, a geotechnical engineer for the state, and sit upon concrete pillars reinforced with tension steel cables. These would allow water and debris from a tsunami to pass underneath while local residents take refuge on the upper floor and roof. Long Beach, Washington, meanwhile, is considering building a berm next to the town’s elementary school. It would normally provide a grassy slope for spectators to watch school sports, but provide shelter for up to 1000 people should a tsunami strike. Sujata Gupta
that happen on the same or neighbouring faults within months of each other. In November 2006, an 8.3-magnitude quake shook the Kuril Islands north of Japan as the Pacific plate pushed beneath them. Two months later, in January 2007, the islands felt the force of a second large quake, this time an 8.1-magnitude event. When the Pacific plate lunged beneath the islands in the first of those quakes, it left the oceanic crust under tension. The January quake was the result of a new rupture that allowed the plate to stretch and thin to compensate (Nature, vol 451, p 561; and see diagram, page 8). Doublets like this show that large earthquakes months apart and on separate faults can be linked by a sound geological mechanism. It does not prove that this is also true of events separated by longer periods and greater
distances. For this, Lay says you would want to show, for instance, that a region which has experienced a large quake recorded unusual seismic activity and perhaps even some small tremors during a previous large event elsewhere on the planet. This might suggest that the earlier event unsettled a fault, effectively priming it. For an example, Lay cites the 7.9-magnitude event that hit Sichuan in China in May 2008. “The 2004 Sumatra earthquake increased seismicity in that area as the [shock] waves passed by,” he says. “Was the 2008 earthquake a delayed, large aftershock, or a totally independent event?” The trouble is that large earthquakes generate tectonic waves that ripple around the world’s surface and routinely trigger smaller quakes on distant faults, so increased activity > 19 March 2011 | NewScientist | 7
SPECIAL REPORT / Japanese quake
Seismic zones shake out nuclear problems
Doublet danger Stretching opens a new fault in the plate, causing a second large quake
“IT’S LIKE a kamikaze terrorist wrapped in bombs just waiting to explode.” That’s how Kobe University seismologist Katsuhiko Ishibashi described Hamaoka, a nuclear power plant situated to the south-east of Tokyo. Straddling the subduction zone between two tectonic plates, it may be the most dangerous nuclear plant in Japan. While that plant was unaffected by the magnitude 9.0 quake on 11 March, the explosions and radiation released at the Fukushima Daiichi nuclear power station this week look set to place the wisdom of siting such plants in quake zones under far greater scrutiny. The UN’s International Atomic Energy Agency says 88 of the world’s 442 nuclear power stations are in seismically active areas – including two in California: the San Onofre plant near San Diego and Diablo Canyon near San Luis Obispo.
STRESSED TECTONIC PLATE RUPTURES KURIL ISLANDS
PACIFIC PLATE TRENCH
15 November 2006 Magnitude
8.3
13 January 2007 Magnitude
8.1
in China is hardly a surprise. “If you have a quake of, let’s say, 6.2 or larger, every sand grain on the planet is moving to the music of that event,” Stein says. Perhaps the biggest stumbling block to proving that large earthquakes trigger others on a global scale is statistics. To find out if quakes really do cluster in a non-random way, Tom Parsons, also at the USGS in Menlo Park, and Aaron Velasco at the University of Texas at El Paso, crunched some numbers. They compensated for the rarity of megaquakes by widening their focus to events of magnitude 7 and higher. The pair then searched for statistical links between these quakes “Meltdown and others of magnitude 5 and above becomes a around the world. risk if water After reviewing a 30-year catalogue evaporates of events, they found no significant faster than it evidence that large quakes regularly trigger tectonic activity 1000 kilometres is pumped into the reactor” or more away. Discussions over the clustering of megaquakes will rumble on. Unfortunately for the people of Japan, what is beyond doubt is that large quakes can cluster locally: aftershocks are common in the wake of a large quake, and occasionally they can be as large as the primary shock. “We are in a cluster right now and it’s centred on Japan,” says Stein. “Japan could be in for other big quakes in the wake of this one. That part we should agree on.” Catherine Brahic n 8 | NewScientist | 19 March 2011
reuters
SUBDUCTION
“Nuclear regulatory agencies will want to re-examine the potential for tsunami risks to nuclear power plants, certainly on the Pacific Rim and possibly in other oceans as well,” says John Stevenson of the IAEA’s International Seismic Safety Centre. While power companies already estimate the risk from tsunamis based on the geological record, Stevenson admits that “there is always the chance that what has been experienced in the past will be exceeded”. That’s what happened at Fukushima. When the quake struck, seismic sensors tripped on the three working reactors, sending neutron-absorbing boron control rods into their cores to shut them down. It doesn’t end there, though. Residual heat from each reactor’s nuclear pile still has to be carried away by the electrically